Dear R People: Here is a small data frame and two particular formulas: > test.df y x 1 -0.9261650 1 2 1.5702700 2 3 0.1673920 3 4 0.7893085 4 5 0.3576875 5 6 -1.4620915 6 7 -0.5506215 7 8 -0.3480292 8 9 -1.2344036 9 10 0.8502660 10 > summary(lm(exp(y)~x))
Call: lm(formula = exp(y) ~ x) Residuals: Min 1Q Median 3Q Max -1.6360 -0.6435 -0.4722 0.4215 2.9127 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 2.1689 0.9782 2.217 0.0574 . x -0.1368 0.1577 -0.868 0.4108 --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Residual standard error: 1.432 on 8 degrees of freedom Multiple R-squared: 0.08604, Adjusted R-squared: -0.0282 F-statistic: 0.7532 on 1 and 8 DF, p-value: 0.4108 > summary(lm(I(y^2)~x)) Call: lm(formula = I(y^2) ~ x) Residuals: Min 1Q Median 3Q Max -0.9584 -0.6387 -0.2651 0.5754 1.4412 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 1.10084 0.62428 1.763 0.116 x -0.03813 0.10061 -0.379 0.715 Residual standard error: 0.9138 on 8 degrees of freedom Multiple R-squared: 0.01764, Adjusted R-squared: -0.1052 F-statistic: 0.1436 on 1 and 8 DF, p-value: 0.7146 > These both work just fine. My question is: when do you know to use I() and just the function of the variable, please? thanks in advance, Sincerely, Erin PS Happy St Pat's Day! -- Erin Hodgess Associate Professor Department of Computer and Mathematical Sciences University of Houston - Downtown mailto: erinm.hodg...@gmail.com ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.